Hundreds of thousands of residents could be left without power for days after vicious storms lashed the eastern US, bringing down electricity lines and resulting in at least 13 deaths.

Officials said it could take up to a week before outages are repaired, leading to fears over the effect that stifling heat could have on old, young and vulnerable people cut off from the relief of air-conditioning.

States of emergency have been declared in Ohio, Virginia, Maryland, the District of Columbia and West Virginia, as forecasters predicted more thunderstorms and temperatures tipping into triple digits in the coming days.

"This is a very dangerous situation," Virginia governor Bob McDonnell said yesterday as he reflected on the largest non-hurricane caused blackouts in the state's history.

Around 3.4 million people have been affected by the power outages, many of them in Washington DC and surrounding areas where temperatures hovered in the high 90s on Saturday.

The sheer scale of the disruption caused to the power grid by the storms caught utility firms unaware, with officials saying that it will take at least a few days to restore lines to all customers.

In New Jersey, governor Chris Christie ordered the National Guard to deliver fuel for generators and fresh waters to areas cut off by the storm.

"The devastation … is very significant," Christie said.

So far, weather conditions have been blamed for 13 deaths – six in Virginia, two in New Jersey, two in Maryland, one in Ohio, one in Kentucky and one in Washington.

In parts of Washington, residents needing assistance were urged to phone non-emergency numbers or travel directly to fire or police stations after 911 response centres were left without electricity.

Authorities also urged some homeowners to start conserving water amid concern over the effect of outages on sewage stations.

Blackouts were reported from Indiana to New Jersey on Saturday, with the bulk of the service interruptions concentrated on the capital.

On Friday, temperatures in DC reached 104F (40°C) – topping a record of 101 set in 1934. Although marginally cooler on Saturday, many were still left sweating as the mercury ticked up into triple digits.

Myra Oppel, a spokeswoman for utility firm Pepco, said engineers were working around the clock to get customers reconnected to electricity.

"We do understand the hardship that this brings, especially with the heat as intense as it is."

More than 20 elderly residents at an apartment home in Indianapolis were evacuated when the facility lost power due to a downed tree.

Most were taken to a Red Cross facility to spend the night, while others who depend on oxygen assistance were given other accommodation, the fire department said.

Meanwhile an Illinois prison was forced to transfer 78 inmates to a new facility after the correction centre was badly damaged in the storm.

The chaos was caused by winds of up to 70mph, which badly disrupted transport routes and knocked out power across the region.

The deaths so far reported in relation to the storm were all thought to be the result of falling trees.

Among those killed was a 90-year-old woman who died when a tree slammed into her home as she slept.

A park police officer was injured by an uprooted tree in northern Virginia county, and an 18-year-old man was struck by a power line. He was in stable condition after receiving CPR, authorities said.

More storms have been predicted, but for now most residents concerns appear to be how to keep cool without home air-conditioners

Those who could afford it flocked to hotels to escape their hot, powerless homes. Others planned to spend the day at places like shopping malls in an effort to get out of the sun.

Jose Amaya, 41, of Germantown, Maryland, was one of millions without power on Saturday.

He said his wife and two daughters planned to go the mall to stay cool, and joked that the outage was going to cost him because they would be shopping. His wife, who works for a hotel chain, also planned to get the family a room to stay.

Robert Clements, 28, said he showered by flashlight on Friday night after power went out at his home in Fairfax, Virginia. Officers at the apartment complex where he lives said power wouldn't be back on for at least two days.

Clements' fiancee, 27-year-old Ann Marie Tropiano, said she tried to go to the pool, but it was closed because there was no electricity so the pumps weren't working. She figured the electricity would eventually come back on, but she awoke to find her thermostat reading 81F (27°C) and slowly climbing. Closing the blinds and curtains didn't help.